1. Field of the Invention
The present invention generally relates to a semiconductor electronic device structure comprising SiCOH (carbon-doped oxides) layers having improved interfacial strength (adhesive and cohesive strength near the interface) to other dielectric or conducting layers. The improved interfacial strength is caused by the presence of transition layers that are formed between the SiCOH layers and the other dielectric or conducting layers. The transition layers are formed in the present invention by starting the deposition of a specific layer, while a surface preparation plasma is still present and active in the reactor. Furthermore, the present invention relates to a method for improving the interfacial strength between different dielectric or conductive layers including those that include Si or C.
2. Description of the Prior Art
The continuous shrinking in dimensions of electronic devices utilized in ULSI circuits in recent years has resulted in increasing the resistance of the BEOL metallization without concomitantly decreasing the interconnect capacitances. Often interconnects are even scaled to higher aspect ratios to mitigate the resistance increases, leading to increased capacitances. This combined effect increases signal delays in ULSI electronic devices. In order to improve the switching performance of future ULSI circuits, low dielectric constant (k) insulators and particularly those with k significantly lower than silicon oxide are being introduced to reduce the capacitance.
The low-k materials that have been considered for applications in ULSI devices include polymers containing Si, C, O, such as methylsiloxane, methylsilsesquioxanes, and other organic and inorganic polymers which are fabricated by spin-on techniques or, Si, C, O and H containing materials (SiCOH, SiOCH, carbon-doped oxides (CDO), silicon-oxycarbides, organosilicate glasses (OSG)) deposited by plasma enhanced chemical vapor deposition (PECVD) techniques. The incorporation of the low-k dielectrics in the interconnect structures of integrated circuits (IC) often requires the use of other dielectric materials as diffusion barrier caps or etch-stop and chemo-mechanical polishing (CMP) hardmasks. The adhesion among the different layers in the complex structures of an IC device is often too low, resulting in delaminations during the processing of the device, or reduced reliability in response to thermomechanical stresses imposed by typical chip packaging materials. Often even when the adhesion is adequate, the deposited low-k film may possess degraded cohesive strength near the initial interface that is formed during deposition, and adhesion testing leads to fracture within this initial layer, which may be from single to single tens of nm thick. Without careful failure analysis, the low failure energies from adhesion testing of such cases may be mistakenly attributed to poor interfacial adhesion, rather than substandard cohesive strength of the near-interface low-k film. This is especially true for interfacial strength (adhesive and cohesive strength near the interface) of a carbon doped oxide dielectric comprised of Si, C, O and H (SiCOH) to other hardmask or diffusion barrier cap dielectics, such as SiN, SiC(H) or SiCN(H).
It would thus be highly desirable to provide a semiconductor device comprising an insulating structure including a multitude of dielectric and conductive layers with good interfacial strength among the different layers, and a method for manufacturing such semiconductor devices.
As described in U.S. Pat. No. 4,647,494, amorphous silicon (a-Si), on the order of tens of Angstroms thick, has been recognized for improving adhesion of wear resistant carbon coatings to metallic magnetic recording layers in recording tapes and disks. That is, a-Si is described in this prior art reference for improving adhesion between amorphous hydrogenated carbon (or diamondlike carbon) and silicide forming metals. Co-pending and co-assigned U.S. application Ser. No. 10/174,748, filed on Jun. 19, 2002 describes semiconductor structures wherein the adhesion between different layers is improved using an interfacial amorphous Si (a-Si) layer.
Despite the above use of a-Si, the adhesion between SiCOH interconnect dielectrics and other layers used in electronic device structures may be affected by the initial layer produced during the deposition of the SiCOH film. The properties of the initial layer may be dependent on the precursor used for the deposition of the film as well as the delay time between the initiation of the precursor flow into the reactor and the initiation of the plasma. Moreover, the initial layer may have different properties than that of the bulk SiCOH film.
As described in U.S. Pat. No. 6,251,770, a first undoped or fluorine-doped initial silicon oxide layer with substantially no carbon can be deposited underneath the carbon-containing organosilicate layer to increase the reactive ion etch selectivity. The organosilicate layer may also include an initial graded region starting from no carbon and increasing to a steady-state carbon level, to improve adhesion to the undoped silicon oxide layer. However adhesion improvement would only require ultrathin layers, which would not be sufficient to alter etch selectivity. Also, to be substantially free of carbon, a separate deposition step with different chemical precursors would be required.
As described in U.S. Pat. No. 6,570,256 a graded carbon layer can be employed within the initial region of a carbon-containing organosilicate layer to improve adhesion to the underlying substrate. However this may not necessarily provide the requisite properties of the organosilicate film near the interface, in particular with respect to adhesion and cohesive strength. If an oxide-like layer is desired within the organosilicate film, there is no means provided to achieve that.
It would thus be further highly desirable to provide a semiconductor device structure and method for manufacturing an insulating structure comprising a multitude of dielectric and conductive layers with improved interfacial strengths between SiCOH layers and other layers in the interconnect structure. It would also be highly desirable to achieve these improved interfacial strengths without introducing additional chemical precursors that would themselves deposit other materials besides the desired SiCOH low-k insulator material, and would allow continuous grading of the interfaces. It would also be highly desirable to achieve the above without introducing additional separate depositions of other film layers.